The present invention relates to an apparatus and method for controlling an ignition timing of an internal combustion engine.
A method for detecting a pressure within the combustion chamber (hereinafter referred to as in-cylinder pressure) of the internal combustion engine (hereinafter referred to as an engine) to control an ignition timing has been proposed. According to a method shown in Japanese Patent Application Unexamined Publication (Kokai) No. 2003-262177, a difference ΔP between the in-cylinder pressure Ptdc at the top dead center (TDC) and the maximum in-cylinder pressure Pmax is compared with a threshold value. If the difference ΔP is less than the threshold value, the ignition timing is advanced.
It is preferable that ignition is performed at an optimum ignition timing. The optimum ignition timing is typically called MBT (Minimum advance for the Best Torque). Ignition at the optimum ignition timing improves the combustion efficiency and the purification performance of exhaust gas.
In general, ignition timings corresponding to various operating conditions of the engine are stored in a memory as a map. The map is referred to based on the detected operating condition of the engine to determine the ignition timing corresponding to the detected operating condition. In a vehicle comprising mechanisms such as a valve timing mechanism and a variable compression ratio mechanism, the number of possible operating conditions of the engine is large, and hence the number of ignition timings to be stored in a map is large. Defining such a large number of ignition timings in a map may be difficult.
Since a recent vehicle comprises various parts associated with the engine, variations may occur in the combustion condition and deterioration over time may vary from part to part. Thus, it may be difficult to establish ignition timings adapted to various parts.
If the optimum ignition timing MBT corresponding to the current operating condition of the engine cannot be determined, the ignition timing needs to be retarded so as to avoid knocking. Control for retarding the ignition timing may reduce the combustion efficiency.
According to the above prior art, the ignition timing is gradually moved to the optimum ignition timing while comparing between the in-cylinder pressure and a threshold value periodically. Since this scheme takes time to cause the ignition timing to converge to the optimum ignition timing, the combustion efficiency may reduce.
Thus, there is a need for an apparatus and a method for estimating the optimum ignition timing MBT corresponding to the current operating condition of the engine and then causing the ignition timing to quickly converge to the estimated optimum ignition timing.